The invention concerns a driving device for automobiles, and more particularly, all-terrain vehicles in which both the front and rear axles are capable of being driven.
In all-wheel driven automobiles of both the passenger automobile and truck types, e.g. four-wheel drive vehicles, an additional center differential between the two driving axles is generally necessary in order to avoid any straining of the drive shafts due to unequal wheel paths, in particular during cornering. Moreover, differential locks are required in general in order to prevent the spinning of individual axles or wheels. These differential locks must be connected manually when needed, in particular during off-the-road driving, but should not be effective during normal road travel conditions. Thus, all-wheel driven vehicles of this kind require not only additional structure and are costly, they can be operated only by expert and specially skilled drivers.
In order to reduce the structural requirements and to render the operation of such all-terrain vehicles easier, driving devices have already been developed (e.g., German Pat. No. 892,275) whereby, in place of the customary center differential, there is provided a transfer case by means of which only one of the drive axles is constantly driven through the interposition of a conventional differential. The other drive axle, in particular the front axle, is usually driven intermittently by the interposition of a freewheel device and another conventional differential, which freewheel device is arranged directly on the transfer case and is automatically lockable. The transmission ratio in the axle drive of the vehicle axle driven by way of the freewheel device is then usually about 2% larger than in the axle drive of the constantly driven vehicle axle. This construction ensures that at normal road conditions only the constantly driven axle, which has no freewheel device, is effective, whereas the drive of the vehicle axle with the freewheel device is connected-in only when one of the wheels of the constantly driven vehicle axle starts to spin. By use of a doubly acting freewheel device, completely automatic switching from two-wheel to four-wheel drive, for example, is obtained in both directions of travel.
While this known driving system is substantially simpler to operate than conventional driving systems because of its automatic connection of the second drive axle, it is still costly from the point of view of the structure needed. In addition to the freewheel device arranged on the transfer case, a conventional differential for the front axle is provided as before, so that in order to achieve a true all-terrain behavior, utilization of a manually actuable, differential lock cannot be dispensed with. Otherwise, under unfavorable conditions it may happen that the wheels of both vehicle axles will spin.